Electrical protective system



March 16, 1965 P. A. AKIN ELECTRICAL PROTECTIVE SYSTEM Filed Dec. 11, 1961 United States Patent O 3,174,143 ELECTRHCAL PROTECTVE SYSTEM Phillip A. Akin, 1522 Strand, Hermosa Beach, Calif. Filed Dec. 11, 1961, Ser. No. 158,474 12 Claims. (Cl. 340-213) The present invention relates to an electrical protective system of the type which includes protective circuitry adapted for sending an alarm signal over a transmission line to a remotely located surveillance station.

One object of the invention is to provide a protective system which is capable of selectively transmitting an oscillating or ilashing signal to a remotely located alarm device.

Another object of the invention is to provide a protective circuit which is adapted to selectively transmit either of two distinctly different types of warnings signals to a remotely located alarm device, the particular type of warning signal indicating the cause of actuation of the protective circuit.

The objects and advantages of the invention will be more readily understood from the following description considered in conjunction with the accompanying drawing, the sole ligure of which illustrates in schematic form an electrical system in which the presently preferred embodiment of the invention is incorporated.

In the accompanying drawing a transmission line which is, preferably, a conventional telephone line, has a pair of input terminals 11, 12 located at an area to be protected while its output terminals 13, 14 are located at a surveillance station. At the surveillance station which may, for example, be the office of a private security police organization, there is an alarm device which provides audible or visual warning signals in response to electrical warning signals applied to the input terminals 11, 12 of the transmission line 10. Alarm device 26 is actuated by a relay coil 21 which is coupled between the output terminals 13, 14 of the transmission line.

In the area to be protected there is located a battery which energizes electrical circuitry whose function it is, under the desired circumstances, to produce electrical warning signals to be supplied to the terminals 11, 12 of the transmission line 10. The general combination of battery-operated protective circuits, a remotely locatd alarm device, and an interconnecting transmission line for actuating the alarm device in response to signals generated by the protective circuits, has been extensively used heretofore. However, the particular arrangement of protective circuits disclosed herein, as well as the functional operation thereof, are believed to be new and unique.

Battery 25 has a negative terminal 26 which is connected through a lead 27 to input terminal 11 of the transmission line. Positive terminal 28 of the battery is connected through a lead 29 to a burglar tape 39 which in turn is serially connected through a holdup switch circuit 35 to the input terminal 12 of the transmission line. Under normal conditions when no warning signal is being generated the circuit is continuous, and battery 25 generates a direct current which is delivered to the relay coil 21 of alarm device 20.

Burglar tape 3l includes serially connected portions filll Patented Mar. 16, 1965 ICC 31, 32, 33 which may be strategically located adjacent respective doors and windows in such manner that the opening of the particular door or window will break the tape, open the circuit, and thus de-nergize relay coil 21 with resultant actuation of the alarm device 20. Holdup switch circuit 35 includes serially connected switches 36, 37 which may be strategically located at4 mains in its normally energized condition, despite anydisruptions or relocations of the burglar tape 30. In similar manner a shorting switch 38 is provided for selectively bypassing the holdup switch circuit 35.

The protective circuits insofar as described in the preceding paragraphs are conventional. However, in accordance with the present invention an oscillator 40 is provided, having terminals 41, 42 and 43 which are interconnected with the previously described portions of the protective circuits, and the cooperative functioning between the oscillator 40 and the remaining circuits is such as to achieve a new and unique operation of the entire protective system.

Terminals 41 and 42 may be considered as the directcurrent input terminals of the oscillator 40, while terminal 43 may be considered as its signal output terminal. Termnial 41 is connected to lead 27 to the negative battery terminal 26, while terminal 42 is connected to the juncture between burglar tape 30 and holdup yswitch circuit 35, and is thus indirectly connected to positive battery terminal 28. Terminal 43 is connected to input lead 12 of the transmission line 10.

During normal operation of the system when all of the holdup switches of circuit 35 are closed the terminal 43 of oscillator 40 is directly tied to terminal 42, hence the 'alternating output -signal of the oscillator is effectively shorted out. However, when any one of the holdup switches is open, the alternating output terminal 43 is no longer tied down, and the oscillator signal is delivered to transmission line 10 and hence to the relay coil 21.

Thus, the following unique mode of operation is achieved. An interruption in burglar tape 30 causes a warning signal to be delivered, the same as if oscillator 40 were not present in the circuit. That is, the ilow of direct current energy to transmission line 1i) is interrupted and relay coil 21 is completely de-energized. But if only the holdup switch circuit 35 is interrupted the direct current energy from the battery continues to ow into the oscillator 40, where it is converted into alternating form, and the energy in alternating form is then delivered through the transmission line 10 to relay coil 21, The operating characteristics of alarm device 20 are selected with reference to the operating frequency of oscillator 40 so as to provide a suitable visual or audible indication at the surveillance station in response to the alternating output of the oscillator, which is readily distinguishable from the visual or audible indication 3 produced when relay coil 21 is completely de-energized.

The significance of this system is that the security police at the surveillance station are immediately able to distinguish between a burglary and a holdup, by virtue of the typ'e of signal generated by alarm device 26. An orf signal indicates a burglary, while a tlas'hing or alternating signal indicates a holdup. A While various types ofnosciilator circuits may be used in accordance with the inventior1`, the oscillator circuit which is presently preferred and which is illustrated herein is a free-running multivibrator. The ,multivibrator 4t) includes a balanced pair of PNP transistors 45 and 46. A resistor47lias one end connected to terminal 42 while its' other end is connected to the emitters of both transistors. lector" of transistor 46 and terminal 41. A bias resistor` 48 is connected between the base of transistor 45 and terminal 4.2 whilea bias resistor 49 is connected between the base of transistor 46 and terminal 42. A coupling capacitor 50 is interconnected between the collector of transistor 45 and the base of transistor 46, and a coupling capacitor 51 is interconnectedV between the base of tran` sistor 45 and the collector of transistor 46. No load resistor as such is provided for transistor 45; rather, the collector of transistor 45 is connected to input terminal 12 of the transmission line 10. It will thus be seen that the transmission line 10, together with its own load, the relay coil 21, is coupled between terminal 41 and the coliector of transistor 45, so as to provide a load for the transistor 45.

The invention has been described in considerable detail in order to comply with the patent laws by providing a full public disclosure of at least one of its forms. However, such detailed description is not intended in any way to limit the broad features or principles of the invention, or the scope of patent monopoly to be granted.

I claim:

1. An alarm system comprising a transmission line having two input terminals and two output terminals; an alarm device coupled between said output terminals; an electronic oscillator having an alternating signal output and a pair of direct-current energy inputs, said signal output and one of said direct-current energy inputs being coupled to respective input terminals of said transmission line; direct-current power supply means coupled between said pairof direct-current energy inputs; and circuit means coupled between said signal output and the other direct-current energy input of said oscillator for normally shorting the output signal of said oscillator so as to deliver substantially the full direct-current potentialV of said direct-current power supply means to said alarm device, but being selectively interruptible for instead permitting the alternating signal generated by said oscillator to be delivered to said alarm device.

2. An alarm system as claimed in claim 1 which further includes additional circuit means coupled in series with said power supply means between said direct-current energy inputs and selectively interruptible for interrupting the ow of direct-current energy to said alarm device.

3. An alarm system as claimed in claim 2 wherein said oscillator is a free-running multivibrator including a pair of cross-coupled electronic switching devices, and a series load impedance coupled to one of said switching devices, said transmission line and alarm device constituting the load for the other of said switching devices.

4. An alarm system as claimed in claim 1 wherein said oscillator is a free-running multivibrator including a pair of cross-coupled electronic switching devices, and a series load impedance coupled to one of said 'switching devices, said transmission line and alarm device constituting the load for the other of said switching devices.

5. An alarm system comprising a transmission line for transmitting an alarm signal to a 'remote location; direct-current power supply means; first and second normally-closed, selectively interruptible circuit means Ar load resistor 52 is coupled between theV col' coupled in series with each other and with said power supply means and the input terminals of said transmission line; and an electronic oscillator coupled in parallel with one of said circuit means for delivering an alternating signal to said transmission line when the associated circuit means is interrupted.

6. An alarm system as claimed in claim 5 wherein said oscillator has a pair of direct-current energy inputs coupled through the other of said circuit means in a series loop con'guration with said power supply means, and an alternating signal output coupled to one input' terminal of said transmission line:

7. An alarm system as claimed' in claim 6 wherein: said oscillator is a free-running multivibrator including a: pair of cross-coupled electronic switching devices, andi a series loadimpedance coupled to one of said switchingi devices, s aid' transmission line andalarm device con stituting the loacl for the other of said' switching devices.

8. An` alarm system as claimed in claim 5 whereinz said oscillator' is a free-running multivibrator including ai pair of crossfcoupledf electronic switching devices, and'. a series load impedance coupled to one of said switching devices, said transmission line and alarm device con-- stituting the load for the other of saidswitching devices;

9. An alarm system for maintaining surveillance of a: protected area, and for producing at a remote station; one of two predetermined types of alarm signals in response to the occurrence of a corresponding condition at the area under surveillance, said alarm system com,- prising, in combination:

an alarm device adapted to be located at the remote` station;

a two-wire transmission line having two input terminals and having two output terminals coupled to said. alarm device;

circuit means adapted to be located at the area underl surveillance, for maintaining said alarm device in al normally energized condition, including direct current power supply means coupled to one of said input terminals, a holdup switchv circuit containingv at least one normally closed holdup switch coupled to the other of said input terminals, and a normally conductive burglar tape circuit coupled in a series loop configuration between said direct current power supply means and said holdup switch circuit;

and an electronic oscillator having a first direct current energy input coupled to said one input terminal of said transmission line, a second direct current energy input coupled to the junction between saidholdup switch circuit and said burglar tape circuit, and a signal output coupled to said other input terminal of said transmission line;

the operation being such that when said normally closed holdup switch is opened the signal from said oscil-A lator passes over said transmission line to cause; said alarm device to produce one type of alarm signal, and when either said transmission line or: said burglar tape circuit is interrupted said alarm device is de-energized for producing another type off alarm signal.

10. An alarm system as claimed in claim 9 wherein` said holdup switch circuit includes at least two normally'- closed holdup switches coupled in series, and which fur-n ther includes a shorting switch coupled in parallel with. said holdup switch circuit.

11. An alarm system as claimed in claim 10 wherein said electronic oscillator includes first and second transistors, the collector of said first transistor being coupled to said signal output, a rst resistor connected between. said second direct current input and the emitters of both of said transistors, a load resistor connected between said lirst direct current input and the collector of said second transistor, iirst and second capacitors coupled between the collector of said tirst transistor and the base of said second transistor, and the collector of said second transistor and the base of said first transistor, respectively, a References Cited by the Examiner second resistor coupled between the base of said rst UNITED STATES PATENTS transistor and said second direct current energy input, 1672 G05 6/28 Sorensen 3,1()147 and a third resistor coupled between the base of said 553:968 5/51 Hauerberg 340 213 second transistor and said second direct current energy 5 2,571,360 10/51 Hauerberg 3,4() 213 input. 2,891,195 6/59 Smyth 307-885 12. An alarm system as claimed in claim 9 which 2,994,013 '7/61 Skele 307-885 further includes a shorting switch coupled in parallel with 3,150,359 9/64 H035 340-213 said burglar tape circuit. 10 NEIL C. READ, Primary Examiner. 

5. AN ALARM SYSTEM COMPRISING A TRANSMISSION LINE FOR TRANSMITTING AN ALARM SIGNAL TO A REMOTE LOCATION; DIRECT-CURRENT POWER SUPPLY MEANS; FIRST AND SECOND NORMALLY-CLOSED, SELECTIVELY INTERRUPTIBLE CIRCUIT MEANS COUPLED IN SERIES WITH EACH OTHER AND WITH SAID POWER SUPPLY MEANS AND THE INPUT TERMINALS OF SAID TRANSMISSION LINE; AND AN ELECTRONIC OSCILLATOR COUPLED IN PARALLEL WITH ONE OF SAID CIRCUIT MEANS FOR DELIVERY AN ALTERNATING SIGNAL TO SAID TRANSMISSION LINE WHEN THE ASSOCIATED CIRCUIT MEANS IS INTERRUPTED. 